A)
Label clean plastic petri
dishes on top and bottom with a unique sequence number and pore size using a
black Sharpie (e.g. 4IR99001, 4IR99002, 4IR99003, etc). The “4” refers to 0.4 mm. The “IR” refers
to the Isle Royale project. The “99” is
the year and “001” is a unique ID number.
B)
Place polycarbonate filters
(47 mm, 0.4 mm) into the dishes. Handle the
filters with all plastic forceps only.
A)
Allow the filters to
equilibrate in the balance room for at least 2 hours before taring. While
equilibrating the partially opened dishes are loosely covered with a clean
plastic bag.
B)
Every seventh filter is
designated as a temperature and humidity control, and is so designated in the
filter log book and on the petri dish. Write
“Control” on the top of the petri dish next to the ID. These filters are kept separate, not to be
taken to the field and not to have anything
filtered through them.
C)
Tare filters on a Perkin
Elmer microbalance (AD‑4) to a significance level of 1 μg after
equilibration for 60 seconds. The balance calibration is recorded in the filter
log book, and is performed with a CLASS M weight before weighing each batch of
filters, and is checked after ever tenth filter. 10% of the filters are re‑weighed. Polonium ionization sources are used to
eliminate static charges.
D)
After filters are used in the
field they are folded in quarters, placed back in the petri dish and are kept
frozen.
E)
When ready to analyze the
filters are dried in a 40°C
oven for at least 48 hours along with at least 10 % control filters (mentioned
in B, above).
F)
Equilibrate the filters in
the balance room as in C.
G)
Weigh filters as in E. This
weight is referred to as ‘post weight 1’.
H)
Place all filters in the oven
again for 24 hours, then equilibrate the filters an in C and weigh the filters
as in E. This second weight is referred to as ‘post weight 2’.
I) Actual sample weight for each session = sample filter weight - original tare weight - the average for all the differences (between post weights and tare weights) of control filters weighed in each session. An average is taken of the actual sample weight in post weight 1 and post weight 2 for final actual sample weight. Concentration of suspended particulate matter (SPM) is then expressed as weight per volume filtered.